g-C3N4@COF heterojunction filler for polymer electrolytes enables fast Li+ transport and high mechanical strength

g-C3N4@COF heterojunction filler for polymer electrolytes enables fast Li+ transport and high mechanical strength | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article g-C3N4@COF heterojunction filler for polymer electrolytes enables fast Li+ transport and high mechanical strength Yongbiao Liu, Yang Song, Yongshang Zhang, Jiande Liu, Lin Li, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4558412/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Solid polymer electrolytes (SPEs) show great promise for high-energy and high-safety lithium metal batteries. However, current SPEs suffer from low ionic conductivity and poor mechanical strength. Herein, the g-C 3 N 4 @COF heterojunction filler is constructed for SPEs for fast Li + transport and high Li + transference number. In addition, a robust 3D network is fabricated by using g-C 3 N 4 @COF heterojunction filler in order to further improve the mechanical robustness and electrochemical stability. As a consequence, the g-C 3 N 4 @COF-3D network/polymer electrolyte displays an ionic conductivity of 1.25×10 − 4 S cm − 1 at 30℃, an electrochemical window of 5.0 V and the tensile strength of 8.613 MPa. Furthermore, assembled LiFePO 4 //Li battery with the g-C 3 N 4 @COF-3D network/polymer electrolyte presents remarkable cycling stability with capacity retention of 99.71% after 600 cycles. Above results indicate the great potential of the g-C 3 N 4 @COF-3D network/polymer electrolyte for advanced energy storage devices. g-C3N4@COF heterojunction filler 3D network Li+ transport mechanical strength solid polymer electrolytes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Lithium metal batteries (LMBs) are considered as promising energy storage devices because of their high energy density. Nevertheless, the practical application of LMBs has been limited due to safety issues associated with the lithium dendrite growth and the flammable characteristic of organic liquid electrolytes [ 1 – 3 ]. Replacing conventional liquid electrolytes with solid-state electrolytes is an effective approach to obtain advanced LMBs with high safety and high energy density [ 4 , 5 ]. Solid polymer electrolytes (SPEs) stand out among variety of solid electrolytes owing to their benign interface contact with electrodes, remarkable mechanical flexibility coupled with processability for large-scale manufacture. However, traditional SPEs show low room-temperature conductivity and poor mechanical strength, which lead to slow Li + transport kinetics and uncontrollable dendrite growth [ 6 – 8 ]. Introduction of nanofillers into SPEs can effectively improve the ionic conductivity by decreasing the crystallinity of polymer matrix and promoting Li + transport at filler/polymer interfaces [ 9 , 10 ]. Besides, construction of robust 3D networks can reinforce SPEs as mechanical support, which can suppress dendrite growth [ 11 – 13 ]. Two-dimensional (2D) fillers could significantly enhance ionic conductivities and simultaneously reinforce polymer electrolytes with improved mechanical strength [ 14 , 15 ]. Carbon nitride (g-C 3 N 4 ) is a kind of typical 2D material with high surface area and electrochemical stability [ 16 , 17 ]. g-C 3 N 4 nanosheets show high specific surface areas and can provide large filler/polymer interfaces, which can provide fast Li + transport pathways, thus improving the ionic conductivity [ 18 , 19 ]. Besides, g-C 3 N 4 nanosheets and polymer matrix have high binding energy, which can considerably reduce interface defects. More importantly, nitrogen atoms in g-C 3 N 4 nanosheets can interact with lithium salts and promote the dissociation of lithium salts [ 20 ]. Furthermore, g-C 3 N 4 nanosheet fillers in composite polymer electrolytes react with lithium metal to form Li 3 N on the surface of lithium metal, which can highly improve the cycling stability [ 21 ]. As a kind of typical porous material, covalent organic frameworks (COFs) show great promise as novel fillers for SPEs because of their porous structure and adjustable chemical properties [ 22 ]. The rich nanoscale pores in COFs can provide ordered nanochannels for rapid Li + transport. In addition, functionalized COFs can have interaction with anions of lithium salt, which could promote the dissociation of lithium salts and generate more free Li + [ 23 , 24 ]. Therefore, introducing nanosized COFs into SPEs demonstrates to be an effective method to improve the Li + transference number. However, nanosized COF powders tend to aggregate in the polymer matrix, which may hinder Li + transport. In this work, g-C 3 N 4 nanosheets with high specific surface area are selected as skeleton for construction of g-C 3 N 4 @COF heterojunction filler for SPEs because of the 2D layered structure and unique chemical properties. The design of the g-C 3 N 4 @COF heterojunction filler can effectively avoid the aggregation of COF nanoparticles. Therefore, the g-C 3 N 4 @COF heterojunction filler can simultaneously achieve fast Li + transport and high Li + transference number. Moreover, a robust 3D network is fabricated based on the g-C 3 N 4 @COF heterojunction filler, which can reinforce the polymer electrolyte with the tensile strength of 8.613 MPa. Consequently, the g-C 3 N 4 @COF-3D network/polymer electrolyte shows superb electrochemical properties, such as an ionic conductivity of 1.25×10 − 4 S cm − 1 at 30℃ and the electrochemical stability window of 5.0 V. In addition, LiFePO 4 //Li batteries assembling with the g-C 3 N 4 @COF-3D network/polymer electrolyte display high cycling stability with capacity retention of 99.71% after 600 cycles. 2. Experiment Preparation of the g-C 3 N 4 @COF heterojunction filler The g-C 3 N 4 was obtained by thermal polymerization of urea. In a typical process, urea was placed in a covered crucible and heated at 550°C for 4 h. After cooling to room temperature, the g-C 3 N 4 was obtained. Then, the mixture of g-C 3 N 4 , melamine and 1,4-Phthalaldehyde with certain mass ratio was dispersed in 20 mL of dimethyl sulfoxide, then the mixture was transferred into a Teflon-lined autoclave and heated at 180 ℃ for 10 h to obrian the g-C 3 N 4 @COF heterojunction filler. Preparation of the composite polymer electrolytes with g-C 3 N 4 @COF heterojunction fillers A certain amount of PEO and g-C 3 N 4 @COF heterojunction filler were mixed uniformly by grinding (where the mass ratio of g-C 3 N 4 @COF heterojunction filler was 10 wt%). LiTFSI was added to the 20 mL of anhydrous acetonitrile to form a solution (with a mass ratio of PEO:LiTFSI:SN of 8:1). Then, the mixture of PEO and g-C 3 N 4 @COF heterojunction filler were introduced into the solution, and the mixed suspension was magnetically stirred at 60°C for 12 h to obtain PEO-based elecrolyte precursor. A certain amount of the PEO-based elecrolyte precursor was transferred to a PTFE mold, and the composite polymer electrolytes with g-C3N4@COF heterojunction fillers could be obtained after heating the PEO-based elecrolyte precursor at 60℃ under vacuum for 24. Preparation of the 3D network The 3D network was fabricated by an electrospinning process. In a typical process, 3 g of PVDF-HFP, 0.25 g of LiTFSI and 0.125 g of g-C 3 N 4 @COF heterojunction filler was added to 10 mL of N,N-dimethylformamide (DMF). The mixture was stirred at room temperature for 12 h to obtain the precursor solution. Electrospinning process was carried out with voltage of 30 kV and distance of 15 cm. The 3D network was obtained by drying under vacuum at 60°C for 12 h. Preparation of the g-C 3 N 4 @COF-3D network/polymer electrolyte A certain amount of PEO and g-C 3 N 4 @COF heterojunction filler were mixed uniformly by grinding (where the mass ratio of g-C 3 N 4 @COF heterojunction filler was 10 wt%). LiTFSI and SN were added to the 20 mL of anhydrous acetonitrile to form a solution (with a mass ratio of PEO:LiTFSI:SN of 8:1:2). Then, the mixture of PEO and g-C 3 N 4 @COF heterojunction filler were introduced into the solution, and the mixed suspension was magnetically stirred at 60°C for 12 h to obtain PEO-based elecrolyte precursor. The 3D network was wet by the PEO-based elecrolyte precursor and dried at 60°C in the vacuum oven for 12 h. This wetting-then-drying process was repeated several times until the 3D network was fully embedded in PEO-based elecrolyte matrix. The fabrication process of the g-C 3 N 4 @COF/polymer electrolyte was similar with that of the g-C 3 N 4 @COF-3D network/polymer electrolyte, and the g-C 3 N 4 @COF/polymer electrolyte was obtained by a typical casting-then-drying approach without 3D network as mechanical support. Other experimental details have been given in supplementary information. 3. Results and discussion The fabrication process of the g-C 3 N 4 @COF-3D network/polymer electrolyte is illustrated as shown in Fig. 1 . First, g-C 3 N 4 nanosheets were prepared by the thermal polymerization of urea. Then the g-C 3 N 4 @COF heterojunction filler could be obtained by in-situ growth of COF nanoparticles on g-C 3 N 4 nanosheets. In order to further reinforce the composite polymer electrolyte, a robust 3D network with high mechanical strength was constructed by using g-C 3 N 4 @COF heterojunction filler as reinforcement phase. Finally, both of the g-C 3 N 4 @COF heterojunction filler and the 3D network were introduced into the polymer electrolyte to fabricate the g-C 3 N 4 @COF-3D network/polymer electrolyte. As shown in Fig. S1 , the g-C 3 N 4 shows a multi-layered structure with thin nanosheets. The unique layered structure endows the g-C 3 N 4 with large surface areas, which can provide large filler/polymer interfaces for fast ion transport. In addition, the nitrogen atoms in surface of the g-C 3 N 4 can absorb TFSI − and thus promote the dissociation of LiTFSI for more mobile Li + . Figure 2 a and 2 b show SEM images of the COF material, which are nanoparticles with uniform size. Figure 2 c and 2 d show SEM images of the g-C 3 N 4 @COF heterojunction filler with the g-C 3 N 4 /COF ratio of 1:1, there is severe agglomeration of COF nanoparticles in g-C 3 N 4 @COF heterojunction filler. The high content of COF leaded to the uneven and uncontrollable COF growth. when the g-C 3 N 4 /COF ratio increased to 1.5:1, COF nanoparticles are uniformly distributed on the nanosheets of g-C 3 N 4 , which can effectively avoid the aggregation of COF nanoparticles in the polymer electrolyte. Moreover, the uniformly distributed COF nanoparticles in g-C 3 N 4 @COF heterojunction filler can promote Li + transport because of nanopores and ordered channels inside COF nanoparticles. Further increasing the g-C 3 N 4 /COF ratio to 2:1, the COF nanoparticles are unevenly distributed on the surface of g-C 3 N 4 nanosheets. The low ratio of COF resulted in limited growth kinetics for COF formation, which leaded to the uneven distribution of COF nanoparticles on the surface of g-C 3 N 4 nanosheets. Figure 3 a shows the XRD patterns of the g-C 3 N 4 , COF nanoparticles and g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios. The as-prepared g-C 3 N 4 exhibits characteristic diffraction peaks at 12.9° and 27.6°, which correspond to (100) and (110) crystal planes of the typical g-C 3 N 4 material, indicating the successful fabrication of the sheet-like g-C 3 N 4 . As for the COF nanoparticle, it shows amorphous nature. Therefore, the diffraction pattern of the g-C 3 N 4 @COF is similar to that of the g-C 3 N 4 , illustrating the amorphous nature of COF nanoparticles. In order to investigate the potential of g-C 3 N 4 @COF heterojunction fillers, composite polymer electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios were constructed. SEM images of the composite polymer electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios are shown in Fig. S2. Figure 3 b shows the XRD patterns of the composite solid electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios. The PEO-LiTFSI electrolyte shows diffraction peaks at 19.0° and 23.3°. After introduction of the g-C 3 N 4 @COF heterojunction fillers, the peak intensity of the composite solid electrolytes decreases to some degree. Of note, the peak intensity of the g-C 3 N 4 @COF(1.5:1)-PEO-LiTFSI electrolyte is the lowest. The decreased peak intensity suggests that g-C 3 N 4 @COF heterojunction filler with g-C 3 N 4 /COF ratio of 1.5:1 can reduce the crystallinity of the polymer electrolyte, thereby promoting the transport of Li + . Moreover, Li + transport of composite solid electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios was investagated, and the testing results are shown in Fig. 3 c. The g-C 3 N 4 @COF(1.5:1)-PEO-LiTFSI electrolyte possesses the smallest ionic impedance, indicating the fastest Li + transport inside the g-C 3 N 4 @COF(1.5:1)-PEO-LiTFSI electrolyte. According to the EIS results, the high-temperature ionic conductivities of composite solid electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios were calculated, respectively. The ionic conductivity of the g-C 3 N 4 @COF(1:1)-PEO-LiTFSI electrolyte is 2.66×10 − 4 S cm − 1 at 60 ℃. And the ionic conductivity of the g-C 3 N 4 @COF(1.5:1)-PEO-LiTFSI electrolyte increases to 4.04×10 − 4 S cm − 1 at 60 ℃. However, with the further decrease of the proportion of the COF to 2:1, the ionic conductivity of the g-C 3 N 4 @COF(2:1)-PEO-LiTFSI electrolyte reduces to 3.26×10 − 4 S cm − 1 at 60 ℃. The EIS results suggest that the optimal g-C 3 N 4 /COF ratio in g-C 3 N 4 @COF heterojunction filler is of 1.5:1, which facilitates the fast Li + transport. In addition, the electrochemical stability of composite solid electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios was tested by linear sweep voltammetry (LSV). All three composite solid electrolytes display remarkable electrochemical stability, their electrochemical windows exceed 4.5 V. Moreover, t (Li + ) (Li + transference number) of the composite polymer electrolytes based on g-C 3 N 4 @COF heterojunction fillers with different g-C 3 N 4 /COF ratios were tested and the results are shown in Fig. 4 . The t (Li + ) of the g-C 3 N 4 @COF(1:1)-PEO-LiTFSI electrolyte is 0.43 (Fig. 4 a), and the t (Li + ) of the g-C 3 N 4 @COF(1.5:1)-PEO-LiTFSI electrolyte increases to 0.47 (Fig. 4 b). For the g-C 3 N 4 @COF(2:1)-PEO-LiTFSI electrolyte, the t (Li + ) decreases to 0.44 (Fig. 4 c). The t (Li + ) testing results indicate that the optimal g-C 3 N 4 /COF ratio in g-C 3 N 4 @COF heterojunction filler is 1.5:1, which helps to realize selective Li + transport. Moreover, in order to further improve the room-temperature ionic conductivity of g-C 3 N 4 @COF-PEO-LiTFSI electrolytes, succinonitrile (SN) was introduced into the composite polymer electrolyte. The corresponding characterization and electrochemical tests are shown in Fig.S4-9. Although the introduction of SN can improve the ionic conductivity, SN simultaneously degrades the mechanical strength and electrochemical stability of the composite polymer electrolyte. Therefore, the robust 3D network was introduced into the composite polymer electrolyte to fabricate the g-C 3 N 4 @COF-3D network/polymer electrolyte. As shown in Fig. 5 a, the 3D network consists of nanofibers and shows a cross-linked structure, the large pores of the 3D network facilitate the infiltration of the polymer electrolyte. More importantly, the robust 3D network can provide mechanical support and reinforce the polymer electrolyte for suppressing lithium dendrite growth. The SEM image of the g-C 3 N 4 @COF-3D network/polymer electrolyte is shown in Fig. 5 b, the polymer electrolyte fills up the 3D network and the 3D network is fully incorporated in the polymer electrolyte. The g-C 3 N 4 @COF-3D network/polymer electrolyte presents a dense and smooth surface without obvious pores and cracks, which can increase the stability and safety of batteries. Besides, XRD patterns of the 3D network, the g-C 3 N 4 @COF/polymer electrolyte and the g-C 3 N 4 @COF-3D network/polymer electrolyte are shown in Fig. 5 c. The 3D network exhibits a characteristic diffraction peak at 20.4°. For g-C 3 N 4 @COF/polymer electrolyte, there are two peaks between 18° to 25°, which reflects the presence of the polymer electrolyte. The diffraction pattern of the g-C 3 N 4 @COF-3D network/polymer electrolyte is similar to that of the g-C 3 N 4 @COF/polymer electrolyte, and there is a peak at 20.4°, reflecting the introduction of the 3D network. Notably, the peak intensity of the g-C 3 N 4 @COF-3D network/polymer electrolyte decreases slightly after introducing the 3D network. The decreased peak intensity of g-C 3 N 4 @COF-3D network/polymer electrolyte suggests that the introduction of the 3D network can reduce the crystallinity of the polymer electrolyte, which helps to promote the transport of Li + . Mechanical strength of polymer electrolytes is of great significance for the safety of cells. Figure 5 d shows stress-strain curves of the g-C 3 N 4 @COF/polymer electrolyte and the g-C 3 N 4 @COF-3D network/polymer electrolyte. The tensile strength of the g-C 3 N 4 @COF/polymer electrolyte is 1.87 MPa. In contrast, after introduction of the 3D network, the tensile strength of g-C 3 N 4 @COF-3D network/polymer electrolyte increases to 8.613 MPa, which helps to inhibit the growth of lithium dendrites for long-life cycle. The ionic conductivities of as-prepared composite electrolytes in this work are estimated by testing electrochemical impedance spectroscopy (EIS). Figure 6 a compares the EIS curves of the g-C 3 N 4 @COF/polymer electrolyte and the g-C 3 N 4 @COF-3D network/polymer electrolyte at 30℃. According to the EIS results, the ionic conductivity of the g-C 3 N 4 @COF/polymer electrolyte is 1.39×10 − 4 S cm − 1 at 30℃. And the ionic conductivity of the g-C 3 N 4 @COF-3D network/polymer electrolyte slightly decreases to 1.25×10 − 4 S cm − 1 at 30℃. Although the introduction of the 3D network sacrifices the ionic conductivity of the composite electrolyte to some degree, the 3D network reinforces the composite electrolyte, which can improve the mechanical strength and the electrochemical stability. Figure 6 b shows LSV curves of the g-C 3 N 4 @COF/polymer electrolyte and the g-C 3 N 4 @COF-3D network/polymer electrolyte, respectively. The electrochemical stability window of the g-C 3 N 4 @COF/polymer electrolyte is 4.6 V. In contrast, electrochemical stability window of the g-C 3 N 4 @COF-3D network/polymer electrolyte reaches up to 5.0 V, indicating the increased electrochemical stability of the g-C 3 N 4 @COF-3D network/polymer electrolyte. The increased electrochemical stability can be attributed to the introduction of the 3D network, which can match high-voltage electrodes for higher energy density. Moreover, Li-Li cells with different electrolytes were fabricated to investigate the t (Li + ), and the corresponding results are as shown in Fig. 6 c and 6 d. The t (Li + ) of the g-C 3 N 4 @COF/polymer electrolyte and the g-C 3 N 4 @COF-3D network/polymer electrolyte are 0.42 and 0.40, respectively. The enhanced t (Li + ) helps to promote homogeneous Li deposition, which plays an important role on inhibition of the dendrite growth. To demonstrate the practical possibility of the g-C 3 N 4 @COF-3D network/polymer electrolyte, LiFePO 4 was selected as the cathode material and lithium metal was selected as the anode material to fabricate LiFePO 4 //Li cells. Figure 7 a displays the charge-discharge curves of the first cycle of as-assembled LiFePO 4 //Li batteries with the g-C 3 N 4 @COF/polymer electrolyte and the g-C 3 N 4 @COF-3D network/polymer electrolyte. The initial discharge specific capacity of the LiFePO 4 //Li battery with the g-C 3 N 4 @COF/polymer electrolyte is 149.17 mA h g − 1 , and the corresponding Coulombic efficiency is 93.38%. The charge-discharge curve is smooth without obvious fluctuation, indicating the reversible electrochemical process. And the LiFePO 4 //Li battery with the g-C 3 N 4 @COF-3D network/polymer electrolyte shows the initial discharge specific capacity of 126.36 mA h g − 1 with the charge-discharge efficiency of 84.18%. Although the LiFePO 4 //Li battery with the g-C 3 N 4 @COF/polymer electrolyte presents higher initial discharge specific capacity and Coulombic efficiency, the cycling stability needs to be further improved. For example, the LiFePO 4 //Li battery with the g-C 3 N 4 @COF/polymer electrolyte maintains a capacity retention of 84.48% after 21 cycles. In contrast, the LiFePO 4 //Li battery with the g-C 3 N 4 @COF-3D network/polymer electrolyte displays remarkable cycling stability with capacity retention of 99.71% after 600 cycles. The above test results demonstrate the considerably enhanced electrochemical stability of the g-C 3 N 4 @COF-3D network/polymer electrolyte for long-life Li metal batteries. The g-C 3 N 4 @COF-3D network/polymer electrolyte shows high mechanical strength, which can effectively suppress the dendrite growth. In addition, the higher electrochemical stability of the g-C 3 N 4 @COF-3D network/polymer electrolyte helps to suppress the side reactions between the solid electrolyte and the electrodes (both of cathode material and lithium metal). 4. Conclusion In conclusion, a novel g-C 3 N 4 @COF heterojunction filler and a robust 3D network were designed and constructed for fabricating composite polymer electrolytes with high ionic conductivity and high mechanical strength. The g-C 3 N 4 @COF heterojunction filler can facilitate rapid and selective Li + transport, thus achieving an ionic conductivity of 1.25×10 − 4 S cm − 1 at 30 ℃ and a t (Li + ) of 0.42. Moreover, the introduction of the robust 3D network significantly improves the mechanical robustness and the electrochemical stability, so the electrochemical window of g-C 3 N 4 @COF-3D network/polymer electrolyte reaches up to 5.0 V and the tensile strength increases to 8.613 MPa. Therefore, LMBs assembled with the g-C 3 N 4 @COF-3D network/polymer electrolyte present great cycling stability. This work indicates the promising prospect of the g-C 3 N 4 @COF heterojunction filler for high-performance SPEs and LMBs. Declarations Competing Interests: The authors declare no competing interests Funding: This work is supported by the foundation of the National Natural Science Foundation of China (82172564), the Doctoral Science Research Foundation of Zhengzhou University of Light Industry (2024BSJJ021, 2022BSJJZK09), the Science and Technology Project of Henan Province-China (2321022411037), Star Space Incubation Project of Zhengzhou University of Light Industry (2021ZCKJ103) and Zhongyuan Scholar Workstation Funded Project (234400510015). Author Contribution Yongbiao Liu: Conceptualization, Investigation, Writing-review & editing. Yang Song:Writing-original draft, Data curation. Yongshang Zhang: Methodology. Jiande Liu: Resources. Lin Li:Writing-original draft. Linsen Zhang: Writing-review & editing, Data curation, Resources. Lulu Du:Writing-review & editing, Data curation, Resources. References Wu F, Maier J, Yu Y (2020) Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries. Chem Soc Rev 49(5): 1569–1614 Liu Y, Zhai Y, Xia Y, Li W, Zhao D (2021) Recent Progress of Porous Materials in Lithium-Metal Batteries. Small Structures 2(5): 2000118 Tan S-J, Wang W-P, Tian Y-F, Xin S, Guo Y-G (2021) Advanced Electrolytes Enabling Safe and Stable Rechargeable Li-Metal Batteries: Progress and Prospects. Adv Funct Mater 31(45): 2105253 Sun C, Liu J, Gong Y, Wilkinson DP, Zhang J (2017) Recent advances in all-solid-state rechargeable lithium batteries. Nano Energy 33: 363–386 Gao Z, Sun H, Fu L, Ye F, Zhang Y, Luo W, Huang Y (2018) Promises, Challenges, and Recent Progress of Inorganic Solid-State Electrolytes for All-Solid-State Lithium Batteries. Adv Mater 30(17): 1705702 Guo B, Wang Q, Wang Z, Meng W, Wang J, Duan H, Guo, H (2024) Enhanced electrochemical performance of PEO/Li 6.4 Ga 0.2 La 3 Zr 2 O 12 composite polymer electrolytes. Ionics. doi: 10.1007/s11581-024-05589-z Li J, Cai Y, Wu H, Yu Z, Yan X, Zhang Q, Bao Z (2021) Polymers in Lithium-Ion and Lithium Metal Batteries. Adv Energy Mater 11(15): 2003239 Fang R, Xu B, Grundish NS, Xia Y, Li Y, Lu C, Goodenough JB (2021) Li 2 S 6 -Integrated PEO-Based Polymer Electrolytes for All-Solid-State Lithium-Metal Batteries. Angew Chem Int Ed 60(32): 17701–17706 Fan L-Z, He H, Nan C-W (2021) Tailoring inorganic-polymer composites for the mass production of solid-state batteries. Nat Rev Mater 6(11): 1003–1019 Yang X, Liu J, Pei N, Chen Z, Li R, Fu L, Zhao J (2023) The Critical Role of Fillers in Composite Polymer Electrolytes for Lithium Battery. Nano-micro Lett 15(1): 74 Du L, Zhang B, Wang X, Dong C, Mai L, Xu L (2023) 3D frameworks in composite polymer Electrolytes: Synthesis, Mechanisms, and applications. Chem Eng J 451: 138787 Du L, Zhang B, Deng W, Cheng Y, Xu L, Mai L (2022) Hierarchically Self-Assembled MOF Network Enables Continuous Ion Transport and High Mechanical Strength. Adv Energy Mater 12(24): 2200501 Wan J, Xie J, Kong X, Liu Z, Liu K, Shi F, Cui Y (2019) Ultrathin, flexible, solid polymer composite electrolyte enabled with aligned nanoporous host for lithium batteries. Nat Nanotechnol 14(7): 705–711 Wen J, Zhao Q, Jiang X, Ji G, Wang R, Lu G, Xu C (2021) Graphene Oxide Enabled Flexible PEO-Based Solid Polymer Electrolyte for All-Solid-State Lithium Metal Battery. ACS Appl Energy Mater 4(4): 3660–3669 Yang Z, Sun Z, Liu C, Li Y, Zhou G, Zuo S, Wu W (2021) Lithiated nanosheets hybridized solid polymer electrolyte to construct Li + conduction highways for advanced all-solid-state lithium battery. J Power Sources 484: 229287 Chen L, Gu T, Ma J, Yang K, Shi P, Biao J, He Y-B (2022) In situ construction of Li 3 N-enriched interface enabling ultra-stable solid-state LiNi 0.8 Co 0.1 Mn 0.1 O 2 /lithium metal batteries. Nano Energy 100: 107470 Wei J, Zheng X, Lin W, Si Y, Ji K, Wang C, Chen M (2022) Retarding Li dendrites growth via introducing porous g-C 3 N 4 into polymer electrolytes for solid-state lithium metal batteries. J Alloys Compd 909: 164825 Sun Z, Li Y, Zhang S, Shi L, Wu H, Bu H, Ding S (2019) g-C 3 N 4 nanosheets enhanced solid polymer electrolytes with excellent electrochemical performance, mechanical properties, and thermal stability. J Mater Chem A 7(18): 11069–11076 Hu J, Chen K, Yao Z, Li C (2021) Unlocking solid-state conversion batteries reinforced by hierarchical microsphere stacked polymer electrolyte. Sci Bull 66(7): 694–707 Liu S, Shen J, Wang Z, Tian W, Han X, Chen Z, Zhu S (2024) Fluorinated carbon nitride with a hierarchical porous structure ameliorating PEO for high-voltage, high-rate solid lithium metal batteries. J Mater Chem A 12(1): 256–266 Xue Z, He D, Xie X (2015) Poly(ethylene oxide)-based electrolytes for lithium-ion batteries. J Mater Chem A 3(38): 19218–19253 Qiao Y, Zeng X, Wang H, Long J, Tian Y, Lan J, Yang X (2023) Application and Research Progress of Covalent Organic Frameworks for Solid-State Electrolytes in Lithium Metal Batteries. Materials, 16(6): 2240 Yuan Y, Zhang Z, Zhang Z, Bang KT, Tian Y, Dang Z, Kim Y (2024) Highly Conductive Imidazolate Covalent Organic Frameworks with Ether Chains as Solid Electrolytes for Lithium Metal Batteries. Angew Chem Int Ed 63(18): e202402202 Yang J, Lin C, Wang Y, Xu Y, Pham DT, Meng X, Lu Y (2024) Enhancing ionic conductivity and suppressing Li dendrite formation in lithium batteries using a vinylene-linked covalent organic framework solid polymer electrolyte. J Mater Chem A 12(3): 1694–1702 Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 15 Jul, 2024 Reviews received at journal 13 Jul, 2024 Reviews received at journal 09 Jul, 2024 Reviews received at journal 06 Jul, 2024 Reviewers agreed at journal 01 Jul, 2024 Reviewers agreed at journal 29 Jun, 2024 Reviewers agreed at journal 22 Jun, 2024 Reviewers invited by journal 16 Jun, 2024 Editor assigned by journal 11 Jun, 2024 Submission checks completed at journal 11 Jun, 2024 First submitted to journal 10 Jun, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4558412","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":317700390,"identity":"46c84fb4-fdfc-4d27-a1b2-5060a3e4d24b","order_by":0,"name":"Yongbiao Liu","email":"","orcid":"","institution":"Shanghai Putailai New Energy Technology Co., Ltd;","correspondingAuthor":false,"prefix":"","firstName":"Yongbiao","middleName":"","lastName":"Liu","suffix":""},{"id":317700391,"identity":"c8ca1f0c-eda3-4900-bb98-c44a862a35b5","order_by":1,"name":"Yang Song","email":"","orcid":"","institution":"Henan Electric Power Transmission \u0026 Transformation Construction CO., Ltd","correspondingAuthor":false,"prefix":"","firstName":"Yang","middleName":"","lastName":"Song","suffix":""},{"id":317700392,"identity":"a86016eb-2d3c-4771-844b-8c0671515fbb","order_by":2,"name":"Yongshang Zhang","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Yongshang","middleName":"","lastName":"Zhang","suffix":""},{"id":317700393,"identity":"c276288c-1a13-4289-b10a-345e94c4ceb5","order_by":3,"name":"Jiande Liu","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Jiande","middleName":"","lastName":"Liu","suffix":""},{"id":317700394,"identity":"6ffdeea8-f307-4666-bdda-6d28f7832c9e","order_by":4,"name":"Lin Li","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Lin","middleName":"","lastName":"Li","suffix":""},{"id":317700395,"identity":"a0e4dd45-eb0b-47af-85eb-97dd2167b04f","order_by":5,"name":"Linsen Zhang","email":"","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":false,"prefix":"","firstName":"Linsen","middleName":"","lastName":"Zhang","suffix":""},{"id":317700396,"identity":"0728cb27-e150-407e-bbba-f1feec2b3a79","order_by":6,"name":"Lulu Du","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuElEQVRIiWNgGAWjYBACPgbmBgYeBhsGAzCXjQgtbAyMIC1pQC3MpGk5TIoWicQ2ibdt5xO3S+QfYPhQdpiBf3YDYS2Sc9tuJ+6ckczAOOPcYQaJOwcIa5Hmbbudu+FGMgMzbxvQhRIJRGk5B9HylwQtByBaGInSwvOw2XLOueT6DWceGxzsOZfOI3GDgBZ+9uSDN96U2RkbHE98+OBHmbUc/wwCWlDAASDmIUH9KBgFo2AUjAJcAADNf0BiT287YAAAAABJRU5ErkJggg==","orcid":"","institution":"Zhengzhou University of Light Industry","correspondingAuthor":true,"prefix":"","firstName":"Lulu","middleName":"","lastName":"Du","suffix":""}],"badges":[],"createdAt":"2024-06-10 13:45:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4558412/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4558412/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59177347,"identity":"ebd4bf79-4c62-4143-86bc-e07e9980d882","added_by":"auto","created_at":"2024-06-27 09:51:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1450160,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the fabrication of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/686293b748254589491d6512.png"},{"id":59177353,"identity":"034c90ed-a347-4f50-9989-5f327d965158","added_by":"auto","created_at":"2024-06-27 09:51:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":502904,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF composites with different C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio: \u003cstrong\u003ea, b\u003c/strong\u003e COF. \u003cstrong\u003ec, d\u003c/strong\u003e g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF=1: 1. \u003cstrong\u003ee, f\u003c/strong\u003e g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF=1.5: 1. \u003cstrong\u003eg, h\u003c/strong\u003e g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF=2: 1\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/365310dafb7911c47ef28638.png"},{"id":59177350,"identity":"01c1f321-fbf6-4978-a631-1853add0ec6e","added_by":"auto","created_at":"2024-06-27 09:51:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":750677,"visible":true,"origin":"","legend":"\u003cp\u003eXRD diffraction patterns: \u003cstrong\u003ea \u003c/strong\u003eg-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios. \u003cstrong\u003eb\u003c/strong\u003e PEO-LiTFSI electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios. \u003cstrong\u003ec\u003c/strong\u003e EIS profiles of PEO-LiTFSI electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios.\u003cstrong\u003e d\u003c/strong\u003e LSV curves of PEO-LiTFSI electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/618d89d9764f9433c6ba8a34.png"},{"id":59177355,"identity":"3c2ed8ff-f0db-410d-baf2-fdd19b314549","added_by":"auto","created_at":"2024-06-27 09:51:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":498232,"visible":true,"origin":"","legend":"\u003cp\u003eCurrent-time curves with the corresponding Nyquist plots before and after polarization: \u003cstrong\u003ea\u003c/strong\u003e The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1:1)-PEO-LiTFSI electrolyte. \u003cstrong\u003eb\u003c/strong\u003e The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1.5:1)-PEO-LiTFSI electrolyte. \u003cstrong\u003ec\u003c/strong\u003e The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(2:1)-PEO-LiTFSI electrolyte.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/217a5c7a5d5cb3778d2c70a4.png"},{"id":59177727,"identity":"a66094fb-80a5-41fb-9798-72f14180333a","added_by":"auto","created_at":"2024-06-27 09:59:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1753344,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eSEM image of the\u003cstrong\u003e \u003c/strong\u003e3D network. \u003cstrong\u003eb \u003c/strong\u003eSEM image of the\u003cstrong\u003e \u003c/strong\u003eg-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. \u003cstrong\u003ec\u003c/strong\u003e XRD patterns of the 3D network, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. \u003cstrong\u003ed\u003c/strong\u003e Stress-strain curves of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/01861c7bc88068e761b8b79f.png"},{"id":59177349,"identity":"da493029-95f6-45d7-82e2-0b92525a996d","added_by":"auto","created_at":"2024-06-27 09:51:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":634217,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Typical EIS plots of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. \u003cstrong\u003eb\u003c/strong\u003e LSV curves of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. Current-time curves with the corresponding Nyquist plots before and after polarization: \u003cstrong\u003ec\u003c/strong\u003e The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. \u003cstrong\u003ed\u003c/strong\u003e The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/9986cd65ab07b1767b515f4b.png"},{"id":59177725,"identity":"e6c04c20-b04e-4e51-a233-8ffb4cd82773","added_by":"auto","created_at":"2024-06-27 09:59:19","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":372610,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Charge and discharge voltage profiles at the first cycle of LiFePO\u003csub\u003e4\u003c/sub\u003e//Li batteries at 0.5 C. \u003cstrong\u003eb\u003c/strong\u003e Cycling performance of LiFePO\u003csub\u003e4\u003c/sub\u003e//Li batteries at 0.5 C.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/3e86f32d79f1221a1725db4d.png"},{"id":59178492,"identity":"994e2bbe-bd5b-4f4d-9e10-ebfd11bfc68b","added_by":"auto","created_at":"2024-06-27 10:07:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7549413,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/0146a624-5670-439e-bd34-20400779d694.pdf"},{"id":59177354,"identity":"fdace36a-2cf8-4be9-b79c-a5cb17fc1207","added_by":"auto","created_at":"2024-06-27 09:51:19","extension":"docx","order_by":9,"title":"","display":"","copyAsset":false,"role":"supplement","size":3054087,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4558412/v1/492dbd06f0e54fa2de00de6f.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"g-C3N4@COF heterojunction filler for polymer electrolytes enables fast Li+ transport and high mechanical strength","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eLithium metal batteries (LMBs) are considered as promising energy storage devices because of their high energy density. Nevertheless, the practical application of LMBs has been limited due to safety issues associated with the lithium dendrite growth and the flammable characteristic of organic liquid electrolytes [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Replacing conventional liquid electrolytes with solid-state electrolytes is an effective approach to obtain advanced LMBs with high safety and high energy density [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Solid polymer electrolytes (SPEs) stand out among variety of solid electrolytes owing to their benign interface contact with electrodes, remarkable mechanical flexibility coupled with processability for large-scale manufacture. However, traditional SPEs show low room-temperature conductivity and poor mechanical strength, which lead to slow Li\u003csup\u003e+\u003c/sup\u003e transport kinetics and uncontrollable dendrite growth [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Introduction of nanofillers into SPEs can effectively improve the ionic conductivity by decreasing the crystallinity of polymer matrix and promoting Li\u003csup\u003e+\u003c/sup\u003e transport at filler/polymer interfaces [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Besides, construction of robust 3D networks can reinforce SPEs as mechanical support, which can suppress dendrite growth [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTwo-dimensional (2D) fillers could significantly enhance ionic conductivities and simultaneously reinforce polymer electrolytes with improved mechanical strength [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Carbon nitride (g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e) is a kind of typical 2D material with high surface area and electrochemical stability [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets show high specific surface areas and can provide large filler/polymer interfaces, which can provide fast Li\u003csup\u003e+\u003c/sup\u003e transport pathways, thus improving the ionic conductivity [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Besides, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets and polymer matrix have high binding energy, which can considerably reduce interface defects. More importantly, nitrogen atoms in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets can interact with lithium salts and promote the dissociation of lithium salts [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Furthermore, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheet fillers in composite polymer electrolytes react with lithium metal to form Li\u003csub\u003e3\u003c/sub\u003eN on the surface of lithium metal, which can highly improve the cycling stability [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs a kind of typical porous material, covalent organic frameworks (COFs) show great promise as novel fillers for SPEs because of their porous structure and adjustable chemical properties [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The rich nanoscale pores in COFs can provide ordered nanochannels for rapid Li\u003csup\u003e+\u003c/sup\u003e transport. In addition, functionalized COFs can have interaction with anions of lithium salt, which could promote the dissociation of lithium salts and generate more free Li\u003csup\u003e+\u003c/sup\u003e [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Therefore, introducing nanosized COFs into SPEs demonstrates to be an effective method to improve the Li\u003csup\u003e+\u003c/sup\u003e transference number. However, nanosized COF powders tend to aggregate in the polymer matrix, which may hinder Li\u003csup\u003e+\u003c/sup\u003e transport.\u003c/p\u003e \u003cp\u003eIn this work, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets with high specific surface area are selected as skeleton for construction of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler for SPEs because of the 2D layered structure and unique chemical properties. The design of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler can effectively avoid the aggregation of COF nanoparticles. Therefore, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler can simultaneously achieve fast Li\u003csup\u003e+\u003c/sup\u003e transport and high Li\u003csup\u003e+\u003c/sup\u003e transference number. Moreover, a robust 3D network is fabricated based on the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler, which can reinforce the polymer electrolyte with the tensile strength of 8.613 MPa. Consequently, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte shows superb electrochemical properties, such as an ionic conductivity of 1.25\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 30℃ and the electrochemical stability window of 5.0 V. In addition, LiFePO\u003csub\u003e4\u003c/sub\u003e//Li batteries assembling with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte display high cycling stability with capacity retention of 99.71% after 600 cycles.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cp\u003e \u003cb\u003ePreparation of the g-C\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eN\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e@COF heterojunction filler\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e was obtained by thermal polymerization of urea. In a typical process, urea was placed in a covered crucible and heated at 550\u0026deg;C for 4 h. After cooling to room temperature, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e was obtained. Then, the mixture of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, melamine and 1,4-Phthalaldehyde with certain mass ratio was dispersed in 20 mL of dimethyl sulfoxide, then the mixture was transferred into a Teflon-lined autoclave and heated at 180 ℃ for 10 h to obrian the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of the composite polymer electrolytes with g-C\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eN\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e@COF heterojunction fillers\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA certain amount of PEO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler were mixed uniformly by grinding (where the mass ratio of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler was 10 wt%). LiTFSI was added to the 20 mL of anhydrous acetonitrile to form a solution (with a mass ratio of PEO:LiTFSI:SN of 8:1). Then, the mixture of PEO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler were introduced into the solution, and the mixed suspension was magnetically stirred at 60\u0026deg;C for 12 h to obtain PEO-based elecrolyte precursor. A certain amount of the PEO-based elecrolyte precursor was transferred to a PTFE mold, and the composite polymer electrolytes with g-C3N4@COF heterojunction fillers could be obtained after heating the PEO-based elecrolyte precursor at 60℃ under vacuum for 24.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of the 3D network\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe 3D network was fabricated by an electrospinning process. In a typical process, 3 g of PVDF-HFP, 0.25 g of LiTFSI and 0.125 g of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler was added to 10 mL of N,N-dimethylformamide (DMF). The mixture was stirred at room temperature for 12 h to obtain the precursor solution. Electrospinning process was carried out with voltage of 30 kV and distance of 15 cm. The 3D network was obtained by drying under vacuum at 60\u0026deg;C for 12 h.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of the g-C\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eN\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e@COF-3D network/polymer electrolyte\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA certain amount of PEO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler were mixed uniformly by grinding (where the mass ratio of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler was 10 wt%). LiTFSI and SN were added to the 20 mL of anhydrous acetonitrile to form a solution (with a mass ratio of PEO:LiTFSI:SN of 8:1:2). Then, the mixture of PEO and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler were introduced into the solution, and the mixed suspension was magnetically stirred at 60\u0026deg;C for 12 h to obtain PEO-based elecrolyte precursor. The 3D network was wet by the PEO-based elecrolyte precursor and dried at 60\u0026deg;C in the vacuum oven for 12 h. This wetting-then-drying process was repeated several times until the 3D network was fully embedded in PEO-based elecrolyte matrix.\u003c/p\u003e \u003cp\u003eThe fabrication process of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte was similar with that of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte, and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte was obtained by a typical casting-then-drying approach without 3D network as mechanical support.\u003c/p\u003e \u003cp\u003eOther experimental details have been given in supplementary information.\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003eThe fabrication process of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte is illustrated as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. First, g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets were prepared by the thermal polymerization of urea. Then the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler could be obtained by in-situ growth of COF nanoparticles on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets. In order to further reinforce the composite polymer electrolyte, a robust 3D network with high mechanical strength was constructed by using g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler as reinforcement phase. Finally, both of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler and the 3D network were introduced into the polymer electrolyte to fabricate the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e shows a multi-layered structure with thin nanosheets. The unique layered structure endows the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e with large surface areas, which can provide large filler/polymer interfaces for fast ion transport. In addition, the nitrogen atoms in surface of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e can absorb TFSI\u003csup\u003e\u0026minus;\u003c/sup\u003e and thus promote the dissociation of LiTFSI for more mobile Li\u003csup\u003e+\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb show SEM images of the COF material, which are nanoparticles with uniform size. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed show SEM images of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio of 1:1, there is severe agglomeration of COF nanoparticles in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler. The high content of COF leaded to the uneven and uncontrollable COF growth.\u003c/p\u003e \u003cp\u003ewhen the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio increased to 1.5:1, COF nanoparticles are uniformly distributed on the nanosheets of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, which can effectively avoid the aggregation of COF nanoparticles in the polymer electrolyte. Moreover, the uniformly distributed COF nanoparticles in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler can promote Li\u003csup\u003e+\u003c/sup\u003e transport because of nanopores and ordered channels inside COF nanoparticles. Further increasing the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio to 2:1, the COF nanoparticles are unevenly distributed on the surface of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets. The low ratio of COF resulted in limited growth kinetics for COF formation, which leaded to the uneven distribution of COF nanoparticles on the surface of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the XRD patterns of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, COF nanoparticles and g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios. The as-prepared g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e exhibits characteristic diffraction peaks at 12.9\u0026deg; and 27.6\u0026deg;, which correspond to (100) and (110) crystal planes of the typical g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e material, indicating the successful fabrication of the sheet-like g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e. As for the COF nanoparticle, it shows amorphous nature. Therefore, the diffraction pattern of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF is similar to that of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, illustrating the amorphous nature of COF nanoparticles. In order to investigate the potential of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers, composite polymer electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios were constructed. SEM images of the composite polymer electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios are shown in Fig. S2.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb shows the XRD patterns of the composite solid electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios. The PEO-LiTFSI electrolyte shows diffraction peaks at 19.0\u0026deg; and 23.3\u0026deg;. After introduction of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers, the peak intensity of the composite solid electrolytes decreases to some degree. Of note, the peak intensity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1.5:1)-PEO-LiTFSI electrolyte is the lowest. The decreased peak intensity suggests that g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler with g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio of 1.5:1 can reduce the crystallinity of the polymer electrolyte, thereby promoting the transport of Li\u003csup\u003e+\u003c/sup\u003e. Moreover, Li\u003csup\u003e+\u003c/sup\u003e transport of composite solid electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios was investagated, and the testing results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1.5:1)-PEO-LiTFSI electrolyte possesses the smallest ionic impedance, indicating the fastest Li\u003csup\u003e+\u003c/sup\u003e transport inside the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1.5:1)-PEO-LiTFSI electrolyte. According to the EIS results, the high-temperature ionic conductivities of composite solid electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios were calculated, respectively. The ionic conductivity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1:1)-PEO-LiTFSI electrolyte is 2.66\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 60 ℃. And the ionic conductivity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1.5:1)-PEO-LiTFSI electrolyte increases to 4.04\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 60 ℃. However, with the further decrease of the proportion of the COF to 2:1, the ionic conductivity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(2:1)-PEO-LiTFSI electrolyte reduces to 3.26\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 60 ℃. The EIS results suggest that the optimal g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler is of 1.5:1, which facilitates the fast Li\u003csup\u003e+\u003c/sup\u003e transport. In addition, the electrochemical stability of composite solid electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios was tested by linear sweep voltammetry (LSV). All three composite solid electrolytes display remarkable electrochemical stability, their electrochemical windows exceed 4.5 V.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMoreover, \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) (Li\u003csup\u003e+\u003c/sup\u003e transference number) of the composite polymer electrolytes based on g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction fillers with different g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratios were tested and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1:1)-PEO-LiTFSI electrolyte is 0.43 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea), and the \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(1.5:1)-PEO-LiTFSI electrolyte increases to 0.47 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). For the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF(2:1)-PEO-LiTFSI electrolyte, the \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) decreases to 0.44 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). The \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) testing results indicate that the optimal g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e/COF ratio in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler is 1.5:1, which helps to realize selective Li\u003csup\u003e+\u003c/sup\u003e transport.\u003c/p\u003e \u003cp\u003eMoreover, in order to further improve the room-temperature ionic conductivity of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-PEO-LiTFSI electrolytes, succinonitrile (SN) was introduced into the composite polymer electrolyte. The corresponding characterization and electrochemical tests are shown in Fig.S4-9. Although the introduction of SN can improve the ionic conductivity, SN simultaneously degrades the mechanical strength and electrochemical stability of the composite polymer electrolyte. Therefore, the robust 3D network was introduced into the composite polymer electrolyte to fabricate the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, the 3D network consists of nanofibers and shows a cross-linked structure, the large pores of the 3D network facilitate the infiltration of the polymer electrolyte. More importantly, the robust 3D network can provide mechanical support and reinforce the polymer electrolyte for suppressing lithium dendrite growth. The SEM image of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the polymer electrolyte fills up the 3D network and the 3D network is fully incorporated in the polymer electrolyte. The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte presents a dense and smooth surface without obvious pores and cracks, which can increase the stability and safety of batteries.\u003c/p\u003e \u003cp\u003eBesides, XRD patterns of the 3D network, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec. The 3D network exhibits a characteristic diffraction peak at 20.4\u0026deg;. For g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte, there are two peaks between 18\u0026deg; to 25\u0026deg;, which reflects the presence of the polymer electrolyte. The diffraction pattern of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte is similar to that of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte, and there is a peak at 20.4\u0026deg;, reflecting the introduction of the 3D network. Notably, the peak intensity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte decreases slightly after introducing the 3D network. The decreased peak intensity of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte suggests that the introduction of the 3D network can reduce the crystallinity of the polymer electrolyte, which helps to promote the transport of Li\u003csup\u003e+\u003c/sup\u003e. Mechanical strength of polymer electrolytes is of great significance for the safety of cells. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed shows stress-strain curves of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. The tensile strength of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte is 1.87 MPa. In contrast, after introduction of the 3D network, the tensile strength of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte increases to 8.613 MPa, which helps to inhibit the growth of lithium dendrites for long-life cycle.\u003c/p\u003e \u003cp\u003eThe ionic conductivities of as-prepared composite electrolytes in this work are estimated by testing electrochemical impedance spectroscopy (EIS). Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea compares the EIS curves of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte at 30℃. According to the EIS results, the ionic conductivity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte is 1.39\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003eat 30℃. And the ionic conductivity of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte slightly decreases to 1.25\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 30℃. Although the introduction of the 3D network sacrifices the ionic conductivity of the composite electrolyte to some degree, the 3D network reinforces the composite electrolyte, which can improve the mechanical strength and the electrochemical stability. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb shows LSV curves of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte, respectively. The electrochemical stability window of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte is 4.6 V. In contrast, electrochemical stability window of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte reaches up to 5.0 V, indicating the increased electrochemical stability of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. The increased electrochemical stability can be attributed to the introduction of the 3D network, which can match high-voltage electrodes for higher energy density.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMoreover, Li-Li cells with different electrolytes were fabricated to investigate the \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e), and the corresponding results are as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed. The \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte are 0.42 and 0.40, respectively. The enhanced \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) helps to promote homogeneous Li deposition, which plays an important role on inhibition of the dendrite growth.\u003c/p\u003e \u003cp\u003eTo demonstrate the practical possibility of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte, LiFePO\u003csub\u003e4\u003c/sub\u003e was selected as the cathode material and lithium metal was selected as the anode material to fabricate LiFePO\u003csub\u003e4\u003c/sub\u003e//Li cells. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea displays the charge-discharge curves of the first cycle of as-assembled LiFePO\u003csub\u003e4\u003c/sub\u003e//Li batteries with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte and the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte. The initial discharge specific capacity of the LiFePO\u003csub\u003e4\u003c/sub\u003e//Li battery with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte is 149.17 mA h g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the corresponding Coulombic efficiency is 93.38%. The charge-discharge curve is smooth without obvious fluctuation, indicating the reversible electrochemical process. And the LiFePO\u003csub\u003e4\u003c/sub\u003e//Li battery with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte shows the initial discharge specific capacity of 126.36 mA h g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with the charge-discharge efficiency of 84.18%. Although the LiFePO\u003csub\u003e4\u003c/sub\u003e//Li battery with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte presents higher initial discharge specific capacity and Coulombic efficiency, the cycling stability needs to be further improved. For example, the LiFePO\u003csub\u003e4\u003c/sub\u003e//Li battery with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF/polymer electrolyte maintains a capacity retention of 84.48% after 21 cycles. In contrast, the LiFePO\u003csub\u003e4\u003c/sub\u003e//Li battery with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte displays remarkable cycling stability with capacity retention of 99.71% after 600 cycles. The above test results demonstrate the considerably enhanced electrochemical stability of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte for long-life Li metal batteries. The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte shows high mechanical strength, which can effectively suppress the dendrite growth. In addition, the higher electrochemical stability of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte helps to suppress the side reactions between the solid electrolyte and the electrodes (both of cathode material and lithium metal).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn conclusion, a novel g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler and a robust 3D network were designed and constructed for fabricating composite polymer electrolytes with high ionic conductivity and high mechanical strength. The g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler can facilitate rapid and selective Li\u003csup\u003e+\u003c/sup\u003e transport, thus achieving an ionic conductivity of 1.25\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 30 ℃ and a \u003cem\u003et\u003c/em\u003e (Li\u003csup\u003e+\u003c/sup\u003e) of 0.42. Moreover, the introduction of the robust 3D network significantly improves the mechanical robustness and the electrochemical stability, so the electrochemical window of g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte reaches up to 5.0 V and the tensile strength increases to 8.613 MPa. Therefore, LMBs assembled with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte present great cycling stability. This work indicates the promising prospect of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler for high-performance SPEs and LMBs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eCompeting Interests:\u003c/strong\u003e \u003cp\u003eThe authors declare no competing interests\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis work is supported by the foundation of the National Natural Science Foundation of China (82172564), the Doctoral Science Research Foundation of Zhengzhou University of Light Industry (2024BSJJ021, 2022BSJJZK09), the Science and Technology Project of Henan Province-China (2321022411037), Star Space Incubation Project of Zhengzhou University of Light Industry (2021ZCKJ103) and Zhongyuan Scholar Workstation Funded Project (234400510015).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eYongbiao Liu: Conceptualization, Investigation, Writing-review \u0026amp; editing. Yang Song:Writing-original draft, Data curation. Yongshang Zhang: Methodology. Jiande Liu: Resources. Lin Li:Writing-original draft. Linsen Zhang: Writing-review \u0026amp; editing, Data curation, Resources. Lulu Du:Writing-review \u0026amp; editing, Data curation, Resources.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWu F, Maier J, Yu Y (2020) Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries. Chem Soc Rev 49(5): 1569\u0026ndash;1614\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu Y, Zhai Y, Xia Y, Li W, Zhao D (2021) Recent Progress of Porous Materials in Lithium-Metal Batteries. Small Structures 2(5): 2000118\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTan S-J, Wang W-P, Tian Y-F, Xin S, Guo Y-G (2021) Advanced Electrolytes Enabling Safe and Stable Rechargeable Li-Metal Batteries: Progress and Prospects. Adv Funct Mater 31(45): 2105253\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun C, Liu J, Gong Y, Wilkinson DP, Zhang J (2017) Recent advances in all-solid-state rechargeable lithium batteries. Nano Energy 33: 363\u0026ndash;386\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao Z, Sun H, Fu L, Ye F, Zhang Y, Luo W, Huang Y (2018) Promises, Challenges, and Recent Progress of Inorganic Solid-State Electrolytes for All-Solid-State Lithium Batteries. Adv Mater 30(17): 1705702\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo B, Wang Q, Wang Z, Meng W, Wang J, Duan H, Guo, H (2024) Enhanced electrochemical performance of PEO/Li\u003csub\u003e6.4\u003c/sub\u003eGa\u003csub\u003e0.2\u003c/sub\u003eLa\u003csub\u003e3\u003c/sub\u003eZr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e composite polymer electrolytes. Ionics. doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s11581-024-05589-z\u003c/span\u003e\u003cspan address=\"10.1007/s11581-024-05589-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi J, Cai Y, Wu H, Yu Z, Yan X, Zhang Q, Bao Z (2021) Polymers in Lithium-Ion and Lithium Metal Batteries. Adv Energy Mater 11(15): 2003239\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFang R, Xu B, Grundish NS, Xia Y, Li Y, Lu C, Goodenough JB (2021) Li\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e6\u003c/sub\u003e-Integrated PEO-Based Polymer Electrolytes for All-Solid-State Lithium-Metal Batteries. Angew Chem Int Ed 60(32): 17701\u0026ndash;17706\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFan L-Z, He H, Nan C-W (2021) Tailoring inorganic-polymer composites for the mass production of solid-state batteries. Nat Rev Mater 6(11): 1003\u0026ndash;1019\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang X, Liu J, Pei N, Chen Z, Li R, Fu L, Zhao J (2023) The Critical Role of Fillers in Composite Polymer Electrolytes for Lithium Battery. Nano-micro Lett 15(1): 74\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDu L, Zhang B, Wang X, Dong C, Mai L, Xu L (2023) 3D frameworks in composite polymer Electrolytes: Synthesis, Mechanisms, and applications. Chem Eng J 451: 138787\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDu L, Zhang B, Deng W, Cheng Y, Xu L, Mai L (2022) Hierarchically Self-Assembled MOF Network Enables Continuous Ion Transport and High Mechanical Strength. Adv Energy Mater 12(24): 2200501\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWan J, Xie J, Kong X, Liu Z, Liu K, Shi F, Cui Y (2019) Ultrathin, flexible, solid polymer composite electrolyte enabled with aligned nanoporous host for lithium batteries. Nat Nanotechnol 14(7): 705\u0026ndash;711\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWen J, Zhao Q, Jiang X, Ji G, Wang R, Lu G, Xu C (2021) Graphene Oxide Enabled Flexible PEO-Based Solid Polymer Electrolyte for All-Solid-State Lithium Metal Battery. ACS Appl Energy Mater 4(4): 3660\u0026ndash;3669\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang Z, Sun Z, Liu C, Li Y, Zhou G, Zuo S, Wu W (2021) Lithiated nanosheets hybridized solid polymer electrolyte to construct Li\u003csup\u003e+\u003c/sup\u003e conduction highways for advanced all-solid-state lithium battery. J Power Sources 484: 229287\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen L, Gu T, Ma J, Yang K, Shi P, Biao J, He Y-B (2022) In situ construction of Li\u003csub\u003e3\u003c/sub\u003eN-enriched interface enabling ultra-stable solid-state LiNi\u003csub\u003e0.8\u003c/sub\u003eCo\u003csub\u003e0.1\u003c/sub\u003eMn\u003csub\u003e0.1\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e/lithium metal batteries. Nano Energy 100: 107470\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWei J, Zheng X, Lin W, Si Y, Ji K, Wang C, Chen M (2022) Retarding Li dendrites growth via introducing porous g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e into polymer electrolytes for solid-state lithium metal batteries. J Alloys Compd 909: 164825\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun Z, Li Y, Zhang S, Shi L, Wu H, Bu H, Ding S (2019) g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e nanosheets enhanced solid polymer electrolytes with excellent electrochemical performance, mechanical properties, and thermal stability. J Mater Chem A 7(18): 11069\u0026ndash;11076\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu J, Chen K, Yao Z, Li C (2021) Unlocking solid-state conversion batteries reinforced by hierarchical microsphere stacked polymer electrolyte. Sci Bull 66(7): 694\u0026ndash;707\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu S, Shen J, Wang Z, Tian W, Han X, Chen Z, Zhu S (2024) Fluorinated carbon nitride with a hierarchical porous structure ameliorating PEO for high-voltage, high-rate solid lithium metal batteries. J Mater Chem A 12(1): 256\u0026ndash;266\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXue Z, He D, Xie X (2015) Poly(ethylene oxide)-based electrolytes for lithium-ion batteries. J Mater Chem A 3(38): 19218\u0026ndash;19253\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiao Y, Zeng X, Wang H, Long J, Tian Y, Lan J, Yang X (2023) Application and Research Progress of Covalent Organic Frameworks for Solid-State Electrolytes in Lithium Metal Batteries. Materials, 16(6): 2240\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan Y, Zhang Z, Zhang Z, Bang KT, Tian Y, Dang Z, Kim Y (2024) Highly Conductive Imidazolate Covalent Organic Frameworks with Ether Chains as Solid Electrolytes for Lithium Metal Batteries. Angew Chem Int Ed 63(18): e202402202\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang J, Lin C, Wang Y, Xu Y, Pham DT, Meng X, Lu Y (2024) Enhancing ionic conductivity and suppressing Li dendrite formation in lithium batteries using a vinylene-linked covalent organic framework solid polymer electrolyte. J Mater Chem A 12(3): 1694\u0026ndash;1702\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"g-C3N4@COF heterojunction filler, 3D network, Li+ transport, mechanical strength, solid polymer electrolytes","lastPublishedDoi":"10.21203/rs.3.rs-4558412/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4558412/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSolid polymer electrolytes (SPEs) show great promise for high-energy and high-safety lithium metal batteries. However, current SPEs suffer from low ionic conductivity and poor mechanical strength. Herein, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler is constructed for SPEs for fast Li\u003csup\u003e+\u003c/sup\u003e transport and high Li\u003csup\u003e+\u003c/sup\u003e transference number. In addition, a robust 3D network is fabricated by using g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF heterojunction filler in order to further improve the mechanical robustness and electrochemical stability. As a consequence, the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte displays an ionic conductivity of 1.25\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 30℃, an electrochemical window of 5.0 V and the tensile strength of 8.613 MPa. Furthermore, assembled LiFePO\u003csub\u003e4\u003c/sub\u003e//Li battery with the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte presents remarkable cycling stability with capacity retention of 99.71% after 600 cycles. Above results indicate the great potential of the g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e@COF-3D network/polymer electrolyte for advanced energy storage devices.\u003c/p\u003e","manuscriptTitle":"g-C3N4@COF heterojunction filler for polymer electrolytes enables fast Li+ transport and high mechanical strength","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-27 09:51:14","doi":"10.21203/rs.3.rs-4558412/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-15T16:36:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-13T05:13:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-09T14:41:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-06T11:12:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"24954375341702221585499365652322762995","date":"2024-07-01T04:03:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"276783055482985755084894360573428229054","date":"2024-06-29T19:03:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"100563073583458817024348994754444050509","date":"2024-06-22T15:48:38+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-16T20:06:18+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-11T23:30:38+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-11T23:29:38+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2024-06-10T13:44:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a64f0566-cede-4f3f-8501-b7ce05260eac","owner":[],"postedDate":"June 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-08-22T16:48:55+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-27 09:51:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4558412","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4558412","identity":"rs-4558412","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}